Question

Given is a table of factors affecting microbial decomposition. (‘$+$’ means ‘favoring’ and ‘$-$’ means inhibiting or lowering). Select the correct option.
A. High temperature- $+$, Lack of oxygen- $+$, Moist environment- $+$, Lignin and chitin in detritus- $-$
B. High temperature- $+$, Lack of oxygen- $-$, Moist environment- $+$, Lignin and chitin in detritus- $-$
C. High temperature- $-$, Lack of oxygen- $-$, Moist environment- $+$, Lignin and chitin in detritus- $-$
D. High temperature- $-$, Lack of oxygen- $+$, Moist environment- $+$, Lignin and chitin in detritus- $-$

Answer 1

Microbial decomposition refers to the breakdown of complex organic matter into simple organic matter which acts as manure for plants. The favoring factors increase the rate of decomposition and inhibiting factors decrease the rate of decomposition. The rate of decomposition depends on various factors of soil and detritus.

Complete answer:
Microbes present in soil metabolize the detritus which is called organic waste to turn it into manure which is used by plants. This process is called microbial decomposition and it depends on several factors of soil and detritus. The $pH$ of the soil, temperature of the soil, moisture of soil, chemical nature of detritus are some factors on which microbial decomposition depends.
Soil temperature around $25{}^\circ$ C is the normal temperature for mineralization of organic waste which completes decomposition in a few weeks or months. The higher the temperature, the faster will be the rate of decomposition. So, a high temperature is a promoting factor.
Oxygen is an essential requirement for aerobic bacteria that causes decomposition. Oxygen promotes aerobiosis. The rate of decomposition increases with more amount of oxygen. Lack of oxygen promotes anaerobiosis which decreases decomposition rate. Thus, the lack of oxygen is an inhibiting factor.
Excessive moisture in soil delays decomposition because it will promote anaerobiosis. Oxygen levels decrease and detritus starts piling up making decomposition slower. But normal moisture level promotes decomposition and is necessary for solubilization of detritus. Hence, a moist environment is a promoting factor up to normal levels.
If chitin and lignin and present in excess in detritus they slow down the process of decomposition. Soils that lack chitin and lignin are rich in nitrogen, sugars, and other water-soluble substances. This makes decomposition faster as compared to lignin and chitin containing detritus. Therefore, lignin and chitin in detritus act as inhibiting factors for decomposition.

Thus, from the above discussion, we can conclude that the right answer is option B.

Note: Decomposition is an important natural phenomenon that ensures the recycling of organic matter in an ecosystem. Decomposers make an important functional unit of an ecosystem. The major decomposers are fungal species. They are the master decomposers that grow on dead and decaying matter and rapidly convert organic waste into usable organic matter.